This invention relates to a method of brazing metal components of low softening temperature to form an assembly, by selectively cooling specific regions of the metal components requiring stabilized configurations during and subsequent to brazing, and to prevent softening and distortion of such specific regions.
More specifically, the invention relates to a method of braze assembling a series of upper and lower cups and connecting tubes, each of which is fabricated from a metal having a low softening temperature, such as copper. Each of the cups has a stepped wall and an annular ring groove for retaining an elastomeric O-ring, upon which a glass tube is seated to provide a tight seal between the glass tube and the metal cup.
Because of the specific nature of the metal components, i.e., having a low softening temperature, a soft solder was heretofore used to join the component copper parts. One of the soft solders employed is identified as Welco No. 5, which comprises 96.5% tin and 3.5% silver, in order to prevent distortion of the specific regions on the metal components. But when the assembled metal components forming series-units were put into use, as elements in a solar collection system, the solder melted out from the joints when a "failure condition" arose in the system employing the units, whereby liquids passing through the units became superheated. To overcome the problem of the solder melting out under a "failure condition", a silver brazing material, either a non-fluxing material or a self-fluxing material was used to obtain a braze that would withstand a "failure condition" in the system employing the units. As anticipated, another problem arose regarding the brazing operation whereby the specific regions requiring dimensional stability became softened and thereby were easily distorted by the heating or by handling during the sealing operation, so that the softening of the metal adversely affected the seal between the glass tubes and the cups.